Reikan Focal - Experience and tips for using with long (400-800mm) lenses?

[mikenott]

I have used Focal for some time. It works extremely well (for me) for lenses up to 300mm. I also recently had my 1Dx body calibrated to my 300 2.8 and 600 f4 (both isII) lenses by Canon and then immediately checked them on Focal and got results around zero AFMA which is reassuring.

However, my 600 f4 isii/1Dx combination produces dodgy looking calibration curves and sometimes fails to produce any curve with extenders. The camera is mounted on a low level Gitzo 3 series tripod with a Wimberley 2 head and the target is the larger pre-printed target mounted on a foam board at a distance of about 100 feet (33 yards, 30 metres). I have attached a couple of images of the curves/data points to show what I mean below.

Has anybody had similar issues with long lenses with Focal and found a solution? Are there any tips you guys can pass on? Any help appreciated.

One is for 600+1.4 and another for 600 +2x

Many Thanks

Michael

 

[Valvebounce]

Hi Michael.
My guess would be light, more light and then some more, you are at f8 with the 2x which is within the reach of the 1Dx for phase af but right at the dark limit, seriously restricting the available af points to the centre cross point and four in a + sensitive to horizontal or vertical lines, (but not both) see pages 82 and 83 of the manual.
It has been noted here several times that FoCal requires lots of light for accurate results even with wider apertures, I have no idea how much light it would require at f8, but I'll bet it's more than my 1500 watts of halogen floods! ;D

Cheers, Graham.

 

[Mt Spokane Photography]

I have used Focal for some time. It works extremely well (for me) for lenses up to 300mm. I also recently had my 1Dx body calibrated to my 300 2.8 and 600 f4 (both isII) lenses by Canon and then immediately checked them on Focal and got results around zero AFMA which is reassuring.

However, my 600 f4 isii/1Dx combination produces dodgy looking calibration curves and sometimes fails to produce any curve with extenders. The camera is mounted on a low level Gitzo 3 series tripod with a Wimberley 2 head and the target is the larger pre-printed target mounted on a foam board at a distance of about 100 feet (33 yards, 30 metres). I have attached a couple of images of the curves/data points to show what I mean below.

Has anybody had similar issues with long lenses with Focal and found a solution? Are there any tips you guys can pass on? Any help appreciated.

One is for 600+1.4 and another for 600 +2x

Many Thanks

Michael

Reikan does have some limits. See the calculator. The large target just barely works with a 800mm lens at 32.2m, but with a TC, it might be restricted to less, it does not give a longer focal length.

http://www.reikan.co.uk/focalweb/index.php/online-tools/test-distance-target-size-calculator/

As you likely know, more light is better. This is mostly due to movement of the lens/ camera for long exposures. Its pretty difficult to keep a setup like that absolutely motionless for a long exposure, and any vibration makes the image look less sharp, throwing their calculations into a tizzy.

 

[dcm]

Mt Spokane is right. I just redid some tests after installing Focal 2. You can't go by Canon's 25x/50x recommendations with Focal if you want the analysis to work. The target needs to be evenly lit and completely fill the spot metering area for Focal to get the exposure right. The tool on the web page provides distance guidelines specific to the Focal implementation based on camera characteristics and target size.

The formulas given on the second page let you compute analysis and target search distances for arbitrary focal lengths. Its a good read if you haven't already looked at it. The analysis distances are within the target search so those are the more important ones. Based on the formulas the analysis ranges for a 1DX are:

600mm: 9.4m to 24.1m
840mm: 13.2m to 33.7m
1200mm: 18.9m to 48.2m

So the 30m distance is a bit long for 600, at the upper limit for 840, and well within the range for 1200. I did my 600 at 24m and got the same results at 30m, probably because my lights covered a broad enough area around the target to fill the spot metering window.

In addition to sufficient light for fast shutter speed some of the key things I found at longer focal lengths are a stable indoor platform (no windage), no image stabilization, and a longer mirror lockup. I tried outdoors but found results inconsistent. For a stable platform and no windage I use the cafeteria at work on a weekend (120ft/36m on a slab floor). I used a mirror lockup delay of 3 seconds which s the default in Focal 2.

I assume you 've got the correct color temp. That affected the results more than I expected when I changed lights and forgot to reset it. You might also change from RAW to JPG to see if that makes a difference, it did for me.

So far I also find the Focal 2 gives me more consistent results with fewer shutter actuations.

 

[mikenott]

Thanks very much fr the feedback - appreciate you all taking the time to reply. Some really good points being made. From what has been said, I am going to try using Focal at closer to the minimum distance, ensure the shutter speed is higher (I have the Pro version), lock up the mirror for at least 3 seconds and double check that the lighting is set correctly on the camera. I tend to do my calibration on (English) summer days (so that means two hot days interrupted by thunderstorms!) and outside (no access to a cafeteria) so can't change the lighting too much, but will note for any winter calibrations.

Will let you know how I get on. Many thanks again!

Michael

 

[Eldar]

For the 600mm, both with and without the extenders, I did a manual AFMA, using a LensAlign unit. It is a simple procedure and it has worked fine. FoCal is very convenient on shorter focal lengths, but I find it less so with the 600 (and longer).

 

[neuroanatomist]

My results with FoCal were fine, although I use manual mode and I oversample. Here's the plot from the 600/4L IS II with the 1.4xIII at 50x focal length (30 m = ~100 feet). FoCal reported EVs of ~15, and my shutter speed was 1/1250 s. I used the standard target (printed on 8.5x11" heavy matte paper).

 

[kaihp]

FoCal reported EVs of ~15

EV of 15 ??? Just how much light is that?
With two 400W floodlights (work lamps) I get barely EV 12, as I recall.

 

[neuroanatomist]

FoCal reported EVs of ~15

EV of 15 ??? Just how much light is that?
With two 400W floodlights (work lamps) I get barely EV 12, as I recall.

Full afternoon sun supplemented with three 150W-equivalent task lamps (20W halogen projector bulbs) at ~12" from the target. Those lights alone give ~12 EV in a dark basement.

 

[kaihp]

FoCal reported EVs of ~15

EV of 15 ??? Just how much light is that?
With two 400W floodlights (work lamps) I get barely EV 12, as I recall.

Full afternoon sun supplemented with three 150W-equivalent task lamps (20W halogen projector bulbs) at ~12" from the target. Those lights alone give ~12 EV in a dark basement.

Interesting. I should try to move the setup outside, if I can find a suitable place to put it and a day without rain (hard to come by, at the moment).

Thanks, Neuro.